● Chrome extension
Manifest V3
local-only

Weave your own headers into every request.

HeaderLoom adds, changes and removes HTTP request headers for API testing and debugging. It runs entirely on your machine, and asks for access only to the sites you add.

Coming soon to Chrome See how it works

No account · No analytics · No remote code · under 100 KB

GET https://api.staging.example/v2/orders

5 rules woven inon api.staging.example

What it does

The page sends one request. Your server sees another.

Chrome applies your rules to each request on the sites you allow, before it leaves the browser. The extension itself never reads your pages or your traffic.

Sent by the pagerequest

GET /v2/orders HTTP/2
host: api.staging.example
accept: application/json
accept-language: en-US
cookie: session=8f2c…
user-agent: Chrome/141

Received by the serverwith HeaderLoom

GET /v2/orders HTTP/2
host: api.staging.example
accept: application/json
accept-language: en-US, frcookie: session=8f2c…user-agent: Chrome/141
authorization: Bearer eyJh…x-env: staging

SetAppendRemove

Built for testing

Small, readable, and quiet.

Everything a header tool needs, and nothing that would make you wonder what else it is doing.

Set, append, remove

Add auth tokens, feature flags or tracing IDs. Append to list headers. Strip what you do not want sent.

Per-site access

No access to every website at install. Chrome asks you to confirm each site when you add it.

Pause in one click

Turn every rule off and on again from the toolbar, without losing your setup.

Bring your rules

Import a ModHeader export file and keep the request headers you already rely on.

Privacy by construction

Your rules never leave the machine.

Rules are kept in Chrome's local storage, not synced and not sent anywhere. Header changes are made by Chrome's own rule engine, so the extension has nothing to see. Read the privacy policy.

account
analytics
remote code
sync
ads

declarativeNetRequestLets Chrome apply your header rules.
storageSaves your rules on this computer.
sites you addOptional. Requested one site at a time, removable whenever you like.

Pricing

Free to use. Pro, once, later.

The free version has no limits on request-header rules. An optional Pro unlock is planned for people who juggle environments.

Free

$0 · forever

Unlimited request-header rules
Set, append and remove
Pause and resume
Per-site access you approve
Import from export files

Pro planned

$19 · one time, no subscription

Multiple profiles, one-click switch
Response-header rules
URL and domain filters, tab-only rules
Export and import profiles as JSON
Active-profile badge on each tab

Pro is not on sale yet. When it is, a merchant of record will be the seller; it will be named here and in the store listing, with the terms and refund policy.

Stop editing requests by hand.

Install HeaderLoom, allow your test site, add a header. That is the whole setup.

Coming soon to Chrome Email support